The present invention relates to an electric drill that has a torque adjusting device which allows the output of strong torque.
A conventional torque adjusting device for an electric drill is shown in FIGS. 1 and 2 and generally includes a motor 1 which has a driving shaft 100 which is engaged with a solar gear system 21 which is composed of three gears 210. The three gears 210 are engaged with an inner toothed periphery 230 of a ring member 23 and a driving part 220 having three rods respectively extending through the three gears 210. The ring member 23 has notches 230 defined in an end thereof and a casing 20 is mounted to the driving part 220. The casing 20 has a tube 24 through which the output shaft 4 extends and the output shaft 4 is securely engaged with the driving part 220. The casing 20 has an annular arranged holes 200 and each hole has a ball 22 received therein which is also engaged with one of the notches 230 of the ring member 23. The casing 20 is received in an adjusting cone 3 which has a spirally stepped shoulder 31 defined in an inner periphery thereof and a compressing ring 32 is engaged with the shoulders 31. A spring 30 is mounted to the tube 24 and the compressing ring 32 and a press ring 33 are respectively located on two ends of the spring 30 wherein the pressing ring 33 seals the holes 200 in the casing 20. As shown in FIG. 3, when the cone 3 is rotated to let a wider portion of the shoulder 31 contact the compressing ring 32 and compresses the spring 30, the balls 22 are securely engaged with the notches 230 so that the ring member 23 is not rotated by the compression force of the balls 22 and the output shaft 4 transforms the torque of the motor 1. When rotating the cone 3 to let a narrower portion of the shoulder 31 contact the compressing ring 32, the spring 30 is applied a smaller force and the balls 22 apply a small force to the ring member 23 so that the ring member 23 can be rotated. Therefore, when the ring member 23 is rotated and the balls 22 are not located in the notches 230, the driving part 220 is not rotated and only the gears 210 rotate about the respective rods. The output shaft 4 at this moment when the balls 22 are not located in the notches outputs the least torque. However, the spring 30 has its largest deformation limitation so that it is difficult to compress the balls 22 to a desired level and this is the reason why the conventional torque adjusting device cannot completely transform the torque of the motor to the output shaft 4.
In accordance with one aspect of the present invention, there is provided a torque adjusting device and comprising a driving part having a plurality of rods and each rod has a gear rotatably mounted thereto. The gears are engaged with a motor""s driving shaft and the driving part is received in an annular member which has a toothed inner periphery engaged with the gears, a plurality of grooves defined longitudinally in an outer periphery of the annular member and a plurality of notches defined in an end of the annular member. A mounting member has a plurality of first passages which are located in alignment with the notches and a ball is received in each of the first passages and engaged with one of the notches. A plurality of second passages are defined through the mounting member and located in alignment with the grooves. Each of second passages has a pin movably received therein and the mounting member has a threaded tube.
An adjusting cap is mounted to the threaded tube and a ring member is fixedly connected to an inside of the cap. The ring member is threadedly mounted to the threaded tube. A first end of a spring is engaged with the ring member and a second of the spring contacts a pressing ring which compresses the balls to engage with the notches. The ring member has contacting parts which push the pins into the grooves when the spring is compressed. An output shaft has an end fixedly connected to the driving part and the other end of the output shaft extends through the threaded tube and the adjusting cap.
The primary object of the present invention is to provide a torque adjusting device for an electric drill wherein the device has pins to be engaged with longitudinal grooves in the annular member so as to output a large torque.
The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention.